The present invention is directed to an optical time integrating correlator which is fabricated in integrated optical form. Integrated optics is rapidly increasing in importance for large bandwidth optical signal processing applications. Some of the advantages of using integrated optical techniques over bulk optical techniques include ease of alignment, ruggedness, freedom from vibration effects, tolerant to temperature changes, small size and low fabrication costs.
In the prior art certain optical processing systems have been constructed using bulk (i.e. discrete) optical components including a time integrating correlator. Such an apparatus is described in an article entitled, "A New Surface-Wave Acoustooptic Time Integrating Correlator", by N. G. Berg et al, App.Physics Lett., 36(4), Feb. 15, 1980, P256-258. It is also described in U.S. Pat. No. 4,326,778. FIG. 1 is an example of such prior art as shown in the cited article in which a laser beam 10 is split into two components via a beamsplitter, a transmitted component 11 and a reflected component 12. These two beams enter a SAW (surface acoustic wave) delay line with a prescribed angle 4.theta..sub.B between them, in which .theta..sub.B denotes the Bragg angle, .theta..sub.B =sin.sup.-1 [.lambda..sub.1 /(2.lambda..sub.a)], where .lambda..sub.1 is the light wavelength and .lambda..sub.a is acoustic wavelength at the design center frequency, so that one beam interacts primarily with SAW.sub.1 while the other beam interacts primarily with the other counterpropagating SAW.sub.2. The resulting diffracted beams 13 and 14 are parallel and overlap. They are imaged onto an integrating detector array for some period of time; the final array output contains the cross correlation of the signals used to generate the two SAWs.
Our present disclosure describes an integrated optical implementation of the time integrating correlator. The integrated device comprises several components including a diode laser, an optical waveguide substrate, a guided-wave lens, an electro-optic beamsplitter, a pair of surface acoustic wave transducers for generating first and second counterpropagating surface acoustic waves, a spatial filter and a detector array.